Fuel starvation during start-up and shut-down processes can adversely affect the performance of proton-exchange membrane fuel cells. In this study, fuel starvation is induced intentionally by supplying hydrogen and air to the negative electrode (anode) side alternately, and the individual electrode potential is measured in situ using a dynamic hydrogen electrode. The positive electrode (cathode) potential is increased to 1.4 V when air/hydrogen boundaries developed on the anode side. The development of a high cathode potential causes oxidation of the carbon support with the amount of CO2 evolution proportional to the cathode potential above 1.0 V. Above similar to 1.2 V, CO and SO2 are generated electrochemically or chemically and the rate of CO production is higher than that of SO2. Although a higher cathode potential is induced irrespective of the cell temperature, oxidation of the carbon support is retarded significantly at low temperatures. (C) 2009 Elsevier B.V. All rights reserved.